Numerical simulation of gasification with a one-dimensional particle submodel for char structure evolution

The exact knowledge of reaction rate, diameter, and density of a char particle is important for precise computational fluid dynamics (CFD) simulations of gasifiers. Most of the present research treats char particles as homogeneous with respect to density and composition. Diameter and density evolve according to power law relations, which are empirical and hard to validate. In this work, char particles are subdivided into multiple homogeneous shell–like volume elements. It allows the calculation of a density profile within the particle and hence profiles of specific surface area and effective diffusivity. This one–dimensional approach is directly compared to the common modeling approach based on Thiele modulus and power law relations. Both have been implemented into a two-dimensional CFD simulation of a lab–scale fixed bed gasifier. Simulations are carried out with particle sizes of 100 μm and 1 mm at temperatures of 800 ◦C up to 1800 ◦C with carbon dioxide and water vapor at 1 atm and 50 atm total pressure. The smaller diameter is relevant for entrained flow gasifiers. The reaction rate can accurately be described by the common approach with slight modifications. However, larger deviations of up to 13% and 42% remain for diameter and density in regimeII. Future work can either employ the presented shell model or adopt the proposed modifications to the common approach.     «

The exact knowledge of reaction rate, diameter, and density of a char particle is important for precise computational fluid dynamics (CFD) simulations of gasifiers. Most of the present research treats char particles as homogeneous with respect to density and composition. Diameter and density evolve according to power law relations, which are empirical and hard to validate. In this work, char particles are subdivided into multiple homogeneous shell–like volume elements. It allows the calculatio...     »